Polymethylmethacrylate bone cements (PMMA bone cements) have been in broad use in medicine for decades for anchoring endoprostheses in bone (Klaus-Dieter Kühn: Knochen-zemente für die Endoprothetik: ein aktueller Vergleich der physikalischen und chemischen Eigenschaften handelsüblicher PMMA-Zemente. Springer Verlag Berlin Heidelberg New York, 2001). In general, polymethylmethacrylate bone cements are made up of a liquid monomer component and a powder component. The liquid monomer component consists of methyl-methacrylate and an activator. N,N-dimethyl-p-toluidine is preferably used as activator. The powder component consists of polymethylmethacrylate or polymethyl-co-acrylmethacrylate, an X-ray contrast agent, and a radical initiator. Zirconium dioxide and barium sulfate are customary X-ray contrast agents. Dibenzoylperoxide is preferably used as radical initiator. After mixing the monomer component and powder component, the bone cement hardens within a few minutes by radical polymerization of the monomer.
After mixing, customary polymethylmethacrylate bone cements are provided in the form of white to pale-yellow pasty masses. This occasionally makes a visual differentiation between bone cement and bone tissue difficult. However, it is desirable to be able to distinguish the bone cement from the surrounding bone tissue without any difficulty. For this reason, Heraeus Kulzer has dyed its PMMA bone cements green with chlorophyll for the past approx. 30 years. However, chlorophyll is only very poorly soluble in the methylmethacrylate monomer used in this context. For this reason, refined peanut oil is added to improve the solubility. The refined peanut oil is free of proteins. However, as with any complex natural product, variations of composition are a problem. No alternatives to refined peanut oil have been identified thus far.
Regarding the dyeing of PMMA bone cements, not only the toxicological non-objectionability of the dye, but also the homogeneous distribution of the dye throughout the cement is important. For this reason, bone cements containing dye pigments in their monomer liquid or powder component have not been widely used thus far. In principle, dye pigments are associated with the risk of the dye pigments being released and migrating from the cement matrix. For this reason, it is particularly important for the dye to be distributed homogeneously in the bone cement and firmly enclosed therein.
It is therefore the object of the invention to develop a dyed PMMA bone cement. The liquid monomer component of the PMMA bone cement shall not contain any complex natural products as solubilizer for dyes that are insoluble or only poorly soluble in methylmethacrylate. The liquid monomer component shall contain a homogeneously distributed dye that is dissolved such as to be translucent.